When the battery is under a situation of abuse such as overcharging, crush or nail penetration, because decomposition of the electrolyte or short-circuit between the positive electrode plate and the negative electrode plate will produce too much heat energy and gas in the power battery and the internal pressure of the power battery will rise sharply, the battery will be fired or exploded. Especially, the prismatic battery is difficult to have a configuration which can cut off or release the current when the heat energy and the internal pressure rise sharply in comparison with the cylindrical battery. Chinese Patent document CN203218343U published on Sep. 25, 2013 discloses a cap assembly for a power battery with an aluminum shell, the positive electrode terminal and the cap plate are electrically connected via a resistor, which makes the aluminum shell and the positive electrode terminal electrically connected, the power battery has an excellent safety performance even if an external short-circuit is established when the power battery with the aluminum shell is under the situation of abuse such as crush, nail penetration and overcharging. Another Chinese Patent document CN102487135A published on Jun. 6, 2012 discloses a rechargeable battery, a resistor is used in combination with a short-circuit member, the resistor is provided in an electrical connection path between the short-circuit member and the positive electrode plate, the external short-circuit current will be decreased when the external short-circuit resistance value is increased due to the resistor, thereby improving the safety performance of the battery.
When the resistance value of the resistor is too small, the external short-circuit current is too large and will break down the cap assembly; when the resistance value of the resistor is too large, the external short-circuit current is too small, which can not decrease the external short-circuit current to a moderate extent when the battery is under the situation of abuse. Conventional single precise resistor with a small resistance value is moderate in resistance value but is not heat-resistant, conventional heat-resistant resistor with a small resistance value is too large in volume, conventional carbon membrane resistor with a small volume is too high in resistance value, therefore a resistor which is moderate in resistance value, small in volume and heat-resistant does not exist in a single lithium battery, and the safety protection mechanism of the single lithium battery can not function well, the dangerous heat energy can not be released in time, for example, the safe reverse valve and the current cutoff mechanism can only inhibit the explosion of the battery, however, they can not release the dangerous heat energy, and the risk of explosion of the battery still exists.